1. Field of the Invention
The present invention relates generally to a scroll type compressor having a seal at the tip of the spiral element. More specifically, the present invention relates to a sealing mechanism to improve durability of the seal.
2. Description of the Related Art
Gaseous fluid compressors have a wide variety of applications such as in an automobile air conditioning system and/or a refrigeration system. A variety of compressor architectures are available for application compatibility. Among those compressors, scroll type compressors have superior work efficiency and are suitable to be employed in a system requiring a small discharge displacement. Japanese Unexamined Patent Publication No. 3-92591 discloses a typical scroll type compressor.
As shown in FIGS. 7 and 8, a conventional scroll type compressor generally includes a fixed scroll 60 having a spiral element 50 that is formed on a end plate 55 and an orbiting scroll 61 is interfitted with the scroll 60. The fixed and orbiting scrolls 60, 61 include spiral elements 50, 51 that are formed on and continuous with the end plate, respectively. The orbiting scroll 61 is eccentrically disposed with respect to the center axis of the fixed scroll 60, and orbits around the above-described axis without self-rotation around its axis while both spiral elements 50, 51 are interfitted to form line contacts. Refrigerant gas is introduced into compression chambers P1, P2 defined by the spiral elements 50, 51 and the end plates 55, respectively. The air-tight compression chambers P1, P2 successively move toward the center portions of the spiral elements 50, 51 according to orbital rotation of the orbiting scroll 61. During the orbiting motion of the scroll 61, the volume of the compression chambers P1, P2 decrease. The compressed gas is discharged to a discharge chamber through a discharge port 54 that is formed in the central portion of the end plate 55 of the fixed scroll 60.
A groove 53 is formed in a tip end surface of the orbiting spiral element 51 that contacts with the fixed end plate 55. A seal 52 is accommodated in the groove 53 for improving air tightness within the compression chamber P1 that is defined by both spiral elements 50, 51. While the refrigerant gas is being compressed, the seal 52 is urged against the surface of the fixed end plate, in order to prevent the refrigerant gas leakage from the high pressurized compression chamber P1 to the low pressurized compression chamber P2. Further, as the compression chamber P1 approaches the discharge port, internal pressure thereof increases. Therefore, the seal 52 includes an enlarged portion 52a that is formed at the central end portion thereof. The enlarged portion 52a improves the air tightness of the compression chamber that is approaching the discharge port.
As shown in FIG. 7, the center of the discharge port 54 of the above-described conventional scroll type compressor is located on a line H that passes through an initial point E of inner peripheral surface S of the fixed spiral element 50 and a center point O.sub.2 of involute generating circle K for generating an involute curve. The line H is perpendicular to the tangent line drawn at the initial point E of the inner peripheral surface S. Therefore, the compressed refrigerant gas is efficiently discharged from the minimized compression chamber P1 in the final compression stage through clearance defined in the vicinity of the initial point E of the discharge port 54.
However, the discharge port 54 is assigned to the fixed location such that the entire discharge port is enabled to be fit within the involute generating circle K. Therefore, a tip portion of the spiral element 51 that forms the minimized compression chamber P1 in the final compression stage covers almost the entire discharge port 54. At this moment, the entire tip portion of the enlarged tip portion 52a confronts against the discharge port 54. The tip portion of the enlarged tip portion 52a tends to bend inward into the discharge port 54 as indicated by a double dotted line in FIG. 8, based upon the suctional action of compressed gas flow. If the tip portion of the seal is repeatedly bent, the tip portion thereof is stressed so that the durability thereof may be lowered. Further, if the above-described case occurs, the tip portion of the enlarged tip portion 52a may hit to the edge of wall portion of the discharge port 54, and may be damaged.